Englewood Marketing Group SH30/52 Series 3000 Replacement Shaving Head, Use For #S3310/81, #S1150/81, #S1560/81 & #S3560/81, Have An Inbuilt Replacement Reminder In The Form Of A Shaving Unit Symbol, Symbol Will Light Up & Indicate You When To Replace Shaving Heads, After Replacing Shaving Heads, You Can Reset The Replacement Reminder By Pressing The On/Off Button For More Than 7 Seconds, Otherwise, Replacement Trigger Will Turn Off Automatically After 9 Successive Shaves.